1. Field of the Invention
The present invention is related generally to an optical communication system, and more particularly to an optical communication system employing grating couplers to provide wavelength division multiplexed data.
2. Description of the Prior Art
Telecommunication systems have employed an optical fiber as the transmission medium. Recent advancements in telecommunications, however, have placed a heavy demand on the total amount of data that can be optically transmitted on a single optical fiber.
For this reason, techniques to multiplex several wavelength channels, each carrying unique data, on to a single optical waveguide, such as a dielectric slab or an optical fiber, have been sought. To achieve wavelength division multiplexing (WDM) it is necessary to couple each wavelength into and out of the optical waveguide without compromising the data carried by the other wavelengths. Adding to this challenge is the constraint that the wavelengths need to be closely spaced so as to all fit within a relatively narrow gain spectrum.
Presently there are commercial wavelength division multiplexed products on the market that utilize for example, array waveguide grating structures, dichroic mirror assemblies, and wavelength selective fiber optic couplers. The products that use these approaches have been refined to yield a performance level that is acceptable for some limited applications. Each approach, however, introduces some compromises in performance. More particularly, in the array waveguide grating approach, such as described in U.S. Pat. No. 5,136,671 by Dragone, a free-space coupling region is fed by an array of individual channeled waveguides that use constructive interference to direct light of a specific wavelength from one waveguide to another waveguide. The constructive interference process is controlled by the propagation path lengths of each waveguide in the coupling array. These path lengths must be accurately maintained to within a fraction of a wavelength of light, and thus this approach requires a high degree of temperature control. In the dichroic mirror assembly approach, light is reflected off wavelength selective mirrors made from multiple dielectic coatings that pass a narrow portion of the optical spectrum and reflect all the remaining portions of the spectrum. The transmitted light of a specific wavelength is coupled to a specific optical output while the other wavelengths are reflected to impinge upon other dichroic mirrors that are designed to pass these wavelengths and couple these wavelengths to their unique optical outputs. To make and assemble dichroic mirrors is extremely complex. In the wavelength selective fiber optic couplers, light of a particular wavelength interacts with an adjacent waveguide within the coupler for the appropriate optical interaction length so as to completely couple over into this adjacent waveguide. The light at other wavelengths remains in the original waveguide and is extracted by another wavelength selective coupler. This approach requires a separate coupler in the optical fiber for each wavelength that is multiplexed. This requires either multiple optical fiber connections or fusion splicing which complicates the manufacturing process. Consequently, the known prior art approaches invoke a high degree of complexity to implement.
What is needed, therefore, is an improved optical system with a single optical waveguide that readily accommodates additional wavelengths for communicating data in a wavelength division multiplexed manner.